The present disclosure relates to a wireless detonator attached to explosives used in tunnel excavation, a wireless detonation system using the wireless detonator, and a wireless detonation method using the wireless detonator.
According to a conventional blasting operation for a tunnel excavation site etc., a plurality of blast holes are drilled in a blasting face which is an excavation surface. A blast hole has, for example, a diameter of approximately several centimeters and a depth, in an excavation direction, of approximately several meters. A wireless detonator, as well as an explosive which can be wirelessly initiated, are both inserted into each of the blast holes. A blasting controller and a blasting controller side antenna are provided in a location remote from the blasting face. The blasting controller and the blasting controller side antenna are used to wirelessly transmit control signals and an initiation signal to the detonator and explosive. The explosives are initiated to blast based on the signal transmitted from a wireless transmitter. For such initiation, various blasting methods are disclosed.
A magnetic field or electric field may be generated around the blasting controller side antenna. Each wireless detonator includes an antenna to receive energy in the form of control signals from the blasting controller, for driving a detonation side electronic circuit utilizing the magnetic field or electric field in a wireless manner. Each wireless detonator receives a wireless control signal (including ID request signal and preparation start signal for an electronic circuit) and an initiation signal to be initiated. Therefore, the antenna of the wireless detonator needs to be capable of performing several functions. The first function needed is to receive energy for driving a detonation side electric circuit. The second function needed is to efficiently receive the wireless control signals and initiation signal. The third function needed is to efficiently transmit a reply signal in response to the received control signals toward the blasting controller.
Examples of such devices are known in the prior art. For example, Japanese Laid-Open Patent Publication No. 2014-134298 (298 publication) describes a wireless detonator having a detonation side antenna (corresponding to an antenna for a wireless detonator) made of a wound coil in a cylindrical shape. The detonation side antenna is arranged within the blast hole so that a longitudinal axial direction of the cylindrical shape coincides with the longitudinal axis of the blast hole.
Japanese Laid-Open Patent Publication No. H08-219700 (700 publication) describes a receiving detonator device (corresponding to the wireless detonator) having a receiving coil (corresponding to the antenna for the wireless detonator). The receiving coil includes a conductive wire wound around an axis corresponding to the longitudinal axial direction of the receiving detonator.
Japanese Laid-Open Patent Publication No. 2001-330400 (400 publication) describes a wireless detonator having a receiving coil (corresponding to the antenna for the wireless detonator). The receiving coil serves to receive an alternating magnetic field energy which is wirelessly transmitted from a blasting controller side antenna.
Japanese Laid-Open Patent Publication No. 2001-153598 (598 publication) describes a wireless detonation unit (corresponding to the wireless detonator) having a receiving coil (corresponding to the antenna for the wireless detonator). The receiving coil serves to receive alternating magnetic field energy which is wirelessly transmitted from a blasting controller side antenna.
Japanese Laid-Open Patent Publication No. 2013-019605 (605 publication) discloses a wireless detonation system having a blasting controller side antenna and a detonation side antenna (corresponding to the antenna for the wireless detonator). The blasting controller side antenna serves as both a transmitting antenna and a receiving antenna for the blasting controller. The detonation side antenna serves as both a transmitting antenna and a receiving antenna for the wireless detonator.
An example of such a device is shown in FIG. 5, including a blasting controller side transmitting antenna 60 that is wound a plurality of times around the perimeter of a planar cross-section of an inner wall of a tunnel. The blasting controller side transmitting antenna 60 is stretched on the inner wall of the tunnel at a position away from the blasting face 41 at a distance L1. The direction of a magnetic field generated around the blasting controller side transmitting antenna 60 is substantially along to the longitudinal direction of the tunnel (in this case, the Z-axis direction), and is orthogonal to the blasting face 41 in the vicinity of a center of the wound blasting controller side transmitting antenna 60 as indicated by the dot chain line in FIG. 3 extending in the Z-axis. However, the direction of the magnetic field in the vicinity of an edge spaced apart from the center of the wound blasting controller side antenna 60 is significantly curved with respect to the direction orthogonal to the blasting face 41. Specifically, in an example of FIG. 5, in an explosive-charge position P2b in the vicinity of the center of the wound blasting controller side transmitting antenna 60, the direction of the magnetic field comprises only a component in the Z-axis direction. Therefore, in this position, the antenna made of a conductive wire wound around the Z-axis direction as an axis can efficiently receive the energy, control signals and initiation signals.
However, according to the example of FIG. 5, for example, in an explosive-charge position P3c, which is a position in the vicinity of the edge of the wound blasting controller side antenna 60, the direction of the magnetic field includes a component in an X-axis direction, a component in a Y-axis direction and a component in the Z-axis direction. In addition, the magnitude of the component in the Z-axis direction may be smaller than the magnitude of the component in the X-axis direction or in the Y-axis direction. Therefore, for example, in the explosive-charge position P3c, the antenna made of the conductive wire wound around the Z-axis direction as an axis cannot efficiently receive the energy, due to directional distortion. Consequently, it does not efficiently receive the wireless control signals and the initiation signals.
According to the disclosures of the 298 publication and the 700 publication, the conductive wire of the antenna for the wireless detonator is wound in a cylindrical manner, and is arranged within the blast hole such that the longitudinal axis-direction of the cylindrical shape in which the conductive wire is wound extends along the longitudinal axis direction of the blast hole (i.e., Z-axis direction in FIG. 5). Therefore, the antenna for the wireless detonator in the vicinity of the center of the wound blasting controller side antenna can efficiently receive the energy as well as the wireless control signals and the initiation signals. However, the region of the antenna for the wireless detonator not near the vicinity of the center of the wound blasting controller side antenna, but rather at the edge of the wound blasting controller side antenna, for the same reasons as described above may not efficiently receive the energy as well as the wireless control signals and the initiation signals.
In the disclosure described in the 400 publication and the 598 publication, descriptions regarding the winding direction of the conductive wire for the receiving coil corresponding to the antenna for the wireless detonator are not found. The antenna may be considered to be made of a conductive wire wound in a cylindrical shape similar to the 298 publication and the 700 publication.
According to the disclosure described in 605 publication, the blasting controller side antenna for the blasting controller serves the dual purpose of both transmitting and receiving signals. Similarly, the detonation side antenna for the wireless detonator serves the dual purpose of both transmitting and receiving signals. Frequencies of the control signals and the initiation signals transmitted from the blasting controller and received by the wireless detonator (operation frequency) are different from the frequency of response signals (response frequency) transmitted from the wireless detonator and received by the blasting controller. The operation frequency is preferably set between 100 kHz to 500 kHz to efficiently feed electric power wirelessly to the wireless detonator (delivery of the energy for ignition and the energy for driving a detonation-side electronic circuit) and to prevent the generation of standing wave. However, in order to act as a dual-purpose device, and also be capable of use to transmit and receive signals efficiently, the band range thereof is limited with respect to the band for the operation frequency. Therefore, it is not possible to freely select the response frequency in accordance with the condition at the site where the wireless detonation system is used. That is, the response frequencies that can be efficiently transmitted and received may be different depending on the condition at the site, and this variable is not accounted for in the flexibility of the band range of the blasting controller.
Therefore, given this context, there is a need for a type of wireless detonator, a wireless detonation system and a method for wireless detonation using the wireless detonator, wherein the wireless detonator can efficiently receive energy, control signals and initiation signals for driving a detonation side electronic circuit without being affected by a positional relation between a blasting controller side antenna and an antenna for the wireless detonator, as well as having a high degree of flexibility in selection of a response frequency of a response signal, and which can efficiently transmit response signals, and which also allows for reduction in size.